1. Field of the Invention
The present invention relates to an ultrasonic microscope which can provide an arbitrary image, such as a B mode image, C mode image or a three-dimensional (3D) image.
2. Description of the Related Art
There is known an ultrasonic microscope which converges an ultrasonic beam into a fine spot, scans a sample with this fine spot with a relative relation between the sample and the spot and processes an echo signal acquired from the sample to thereby observe the internal conditions of the sample.
FIG. 12 exemplifies the structure of a conventional ultrasonic microscope. An ultrasonic burst wave produced from a high frequency transmitting section 101 is applied to a piezo-electric transducer (ultrasonic transducer) 103 through a circulator 102. The transducer 103 converts a high frequency electric signal into an ultrasonic wave. This ultrasonic wave is converted into a convergent spherical wave by an acoustic lens 104 and is converged into a fine spot. The converted spherical wave enters a sample 105 disposed at the proximity of the focusing plane.
The space between the acoustic lens 104 and sample 105 is filled with a coupler liquid which serves to propagate an ultrasonic wave. The ultrasonic pulse incident to the sample 105 undergoes an influence such as reflection, penetration, scattering or absorption. The ultrasonic wave reflected from the sample 105 propagates again through the coupler liquid 106 passes through the acoustic lens 104, then is converted into an electric signal by the piezo-electric transducer 103. The electric signal travels through the circulator 102 to a high frequency amplifier 109 for amplification. The unnecessary signal component of the amplified signal is eliminated by a gate 110, which is controlled by a controller 108. As a result, only the necessary echo signal from the sample 105 is extracted and is led to a detector 111. The detector 111 subjects the echo signal to envelope detection to acquire the intensity of the echo signal. The resultant signal is subjected to signal processing in a video processor 112, then written into an image memory 113.
The above description is concerned with point data of the sample 105. A scanner 107 is provided to acquire two-dimensional (2D) image data. The scanner 107 executes 2D scanning on the sample 105 with an ultrasonic pulse, and data of each point is similarly stored in the image memory 113. In order to confirm or view the internal image of the sample 105, the data needs to be read out from the image memory 113 and displayed on a monitor 114.
The image acquired by this prior art technique is a so-called C mode (or C scope) image. That is, with the emitting direction of an ultrasonic pulse taken on the z axis and two axes normal to the z axis being x and y axes, an image acquired through x-y scanning by the scanner 107 is a 2D image of a plane of the sample 105 parallel to the x-y plane. This mode cannot provide date of different internal portions of the sample at different depths. In order to acquire internal data of a sample at different depths, it is necessary to acquire another C mode image which has undergone z-directional scanning in addition to the x-y scanning to reflect an altered relationship between the sample 105 and the converging position of the ultrasonic pulse. This method complicates the scanning.
An ultrasonic tomographic apparatus is conventionally known to provide a tomographic image of a plane parallel to an emitted ultrasonic pulse, i.e., a B mode (or B scope) image. This type of apparatus cannot however provide a C mode image nor a 3D image.
The aforementioned conventional ultrasonic microscope and tomographic apparatus are both for attaining 2D image data. No apparatuses have been realized at present which provide image data reflecting the acoustic property of a 3D structure. For instance, in order to observe a 3D distribution of defects inside a sample, the shape of a heterogeneous medium or the like, it is desirable that not only one tomographic plane of a sample but also a 3D projection image of the sample be easily acquired.